Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.35	10.588%	$136.4103	$136.41	$136.40	$136.40
Purchase #2	$121.60	7.838%	$131.131	$131.13	$131.15	$131.10
Purchase #3	$111.25	12.726%	$125.4077	$125.41	$125.40	$125.40
Purchase #4	$99.85	5.240%	$105.0821	$105.08	$105.10	$105.10
Purchase #5	$223.60	4.251%	$233.1052	$233.11	$233.10	$233.10
Purchase #6	$36.60	7.348%	$39.2894	$39.29	$39.30	$39.30
Purchase #7	$20.33	12.603%	$22.8922	$22.89	$22.90	$22.90
7 purchase totals =	$736.58		$793.3179	$793.32	$793.35	$793.30